Water hyacinth (Eichhornia sp.) is a genus of noxious aquatic weeds. The genus includes the species Eichhornia azurea, Eichhornia crassipes, Eichhornia diversifolia, Eichhornia paniculata. In India, more than 200,000 ha of water surface is infected by plants from this genus. It poses serious economic, social and environmental problems in India and many countries in tropics and subtropics. It shows that the plant's reproductive capacity, adaptability, nutritional requirements and resistance to adverse environments make it impossible to eradicate, and difficult to control. The problem of the spread of water hyacinth in the waterways and banks, which causes them to waste water by increasing the rate of transpiration and great rival for fish and plankton and then change the natural qualities of water as a result of the decomposition of the plant and the consumption of dissolved oxygen and thus aquatic life. It is a free-floating aquatic macrophyte, reproducing both vegetatively via ramets formed from axillary buds on stolons, and sexually through seed production.
A variety of methods have been tried to curb the growth of the weed. Herbicides are used most often, because they provide an immediate action tool, although, they are costly and may have toxic effects if not applied according to the manufacturers' instructions. There is currently much concern about the use of synthetic chemical herbicides, such as glyphosate, to control weeds. Consequently, the use of synthetic chemical herbicides is already barred or restricted in many areas of world.
Because of the reproductive capacity and fast growth of water hyacinth, it has been necessary to use a set of biocontrol agents to increase the biotic stress in order to reduce population resurgence. Among the natural enemies of water hyacinth, plant pathogens and its metabolites can be useful because, they are often host-specific (no risk to crops, native plants or animals), easy to propagate and disseminate and self-maintaining, thus reducing the need for repeated applications. However as is the case for other biopesticides, microbial herbicides are inactivated in the environment by exposure to temperature, low humidity and ultraviolet radiation. In fact, the main problem of biopesticides is their large-scale production in a formulation that allows for a successful application in the field. Among plant pathogens, fungi are the most important natural plant pathogens. Many fungal pathogens have been cited in the literature as potential biocontrol agents for water hyacinth. Among them are Cercosporapia ropi (=C. rodmanii), Acremonium zonatum, Alternaria eichhorniae, Myrothecium roridum, Rhizoctonia solani and Uredo eichhorniae. A. eichhorniae and C. piaropi, have been studied for their biology, biocontrol potential, host specificity formulation and have been tested in experimental conditions.
However, no commercial bioherbicide for water hyacinth is available. Biological control reduces weed vigour, combined with environmental conditions, phenology of the plant and integrated use of other management options. The use of bioherbicides as biocontrol agents is therefore attracting considerable attention. Bioherbicides are typically endemic and applied inundatively to control undesired vegetation. In particular, mycoherbicides are bioherbicides based on fungal plant pathogens. The principal objective in dealing with weeds is to reduce competition from the weeds so as to allow the desired plants to grow freely. Accordingly, biocontrol of weeds addresses concerns about the effects of chemicals on environmental integrity and human health.